Since the early 19th century, the term shortening has been used to mean fats or oils that “shorten” a dough, or weaken its structure and thus make the final product more tender or flaky. This role is most evident in pie crusts and puff pastry, where layers of solid fat separate thin layers of dough from each other so that they cook into separate layers of pastry. It’s less evident but also important in cakes and enriched breads, where fat and oil molecules bond to parts of the gluten protein coils and prevent the proteins from forming a strong gluten. To make a rich bread with a strong gluten (e.g. Italian panettone), the baker mixes the flour and water alone, kneads the mix to develop the gluten, and only then works in the fat.